The present invention is directed generally to removing broken threaded members, such as bolts or other fasteners, from a body. More particularly, the invention is directed to removing broken threaded environmental sensor bodies from equipment, such as a thermocouple from a heat exchanger.
Often a head of a threaded fastener, such as bolt, will break off of a shaft of the fastener while the fastener is threaded in a tapped mated hole in a piece of equipment. The removal of the shaft remaining in the hole is a difficult process that often results in damage to the equipment. Generally, a bore must be drilled in the shaft of the broken fastener to provide access for a removal tool.
The most commonly used tool for removing the fastener shafts is known as an "easy-out". The easy-out is a cylindrical tool that is tapered to provide a continuous decreasing cross-section from a drive head to an insertion end of the tool. The tool body has edges or fluted threads running in a direction opposite to the thread direction in the tapped hole. When the tool is inserted in the bore, the edges or threads engage the bore walls near the broken edge of the fastener. A force is applied to the drive head to remove the fastener from the tapped hole. The tapered design of the easy-out allows for its use with a wide range of bore sizes.
U.S. Pat. Nos. 4,604,917, 4,777,850 and 5,031,487issued to Polonsky disclose combination drill bit/removal tool devices that provide for drilling the bore in the shaft, inserting a removal tool and extracting the broken fastener in a stepwise continuous process. The removal tool portion is a tapered device that engages the bore wall at the broken edge of the shaft, similar to the easy-out tools. A difficulty with the easy-out tools and the combination tools of Polonsky is that the tapered shape of the tools provides for a very small contact area with the bore wall at the broken end of the shaft. Therefore, the torque required to loosen the entire fastener must be translated through the very small contact area. As might be expected, the concentrated application of torque to the small area often causes the fastener material to yield and the tool strips the bore, or the easy-out itself breaks off in the bore. As a result, it may take several iterations before the fastener is removed, or, worse yet, the removal attempt may be unsuccessful.
Recognizing the aforementioned difficulties, U.S. Pat. Nos. 4,831,902 (the "'902 patent") and 5,279,187 (the "'187 patent") provide broken fastener removal devices that provide extended contact areas between the removal tool and the shaft of the fastener. The '902 patent discloses the use of a plurality of bore holes drilled in the shaft to attach a removal tool. A corresponding number of alignment pins are inserted into the bore holes and connected to a drive head that is used to remove the fastener. In the '902 patent embodiments, a substantial shearing force is exerted upon the alignment pins at the broken end of the shaft. Therefore, the pins must have sufficient strength to withstand the shearing force at the edge of the shaft, while being of a small enough dimension that a plurality of the pins can be inserted in the shaft. Also, these devices cannot be easily adapted for use in removing tubular fasteners, such as sensor bodies.
The '187 patent provides an expandable jaw removal tool for use in removing broken fasteners. The expandable jaw is inserted into a previously drilled bore in the shaft. The jaws are expanded to contact the bore wall and translate an applied torque to remove the fastener. The invention of the '187 patent provides a viable option for removing broken fasteners. However, it may be difficult to remove fasteners that are not only broken, but mechanically frozen in the tapped hole using the techniques of the '187 patent.
In view of these and other difficulties with prior art removal tools and methods, there is a need for more versatile tools and methods for removing broken threaded members from tapped holes.